Chartplotters

Chart plotters give a visual chart display, and when linked to a GPS will show your position. They can also be used to create waypoints and can be part of an integrated system that will show other data.

How they workFor yachtsmen with an extensive range of paper charts, the original chart plotter which started the navigation revolution – the Yeoman – might be ideal.
It uses paper charts fixed to an electronic board, and as you move the cursor around the board the changing lat and long is displayed on a screen. Plotters with charts stored on cartridges work on the same principle.
To create waypoints all you do is zoom in and click the cursor and the lat and long is stored. So to make a route you just drag and click across the chart. This saves all the mistakes of transferring positions from a paper chart into a GPS memory.

What to look out for
No display is as big as a paper chart and big screens cost more money. For sailors who navigate on paper charts and just use a chart plotter as a ‘visual position reminder’, then a small screen is fine – as long as you are happy zooming in and out. Mono screens used to be easier to read in direct sunlight, but colour screens have improved and make details much clearer. However, do check that small details on the chart are clear, as some screens are quite pixelated.
Also check that the symbols are to your liking, because the same chart cartridge in two different makes of chart plotter can create different symbols. The rate at which the charts redraw is worth checking, by scrolling north/south and east/west. Also try zooming in and out quickly.

Charts
These come in two formats, raster and vector. Raster charts are electronic copies of a paper chart but vector charts are made up of layers which can be turned on and off to make things clearer. If you are not sailing at night, for example, you can switch off all the light symbols for clarity. On some sets the lights that are within range of your position at night will start to flash with the correct characteristics. And if you are using the chart plotter combined with a radar overlay, it is often clearer if the main chart is under the radar image and then there is another layer on top of that, showing just a black coast outline with the navigation marks.

Graphics
More information is being added to electronic charts all the time – many now have satellite images that can be overlaid on the chart, aerial photographs, 3D displays of land contours that can be viewed from different angles and also 3D views of the sea bed.
Obviously the basic charts don’t have all these ‘bells and whistles’ but it is worth comparing the different graphical styles of each cartography manufacturer. Most will only work with one type of cartography and this might influence which plotter you buy. Also check the areas covered by each chart cartridge – some makes might cover your cruising area more economically than others.